A new fluorescent nanosensor for the selective determination and differentiation of Fe³⁺, Bi³⁺ and Al³⁺ was reported based on dual-emission carbon nanodots (DECNDs), which contained blue emitters (λ_ex = 315 nm, λ_em = 386 nm) and yellow emitters (λ_ex = 365 nm, λ_em = 530 nm). In this assay, Fe³⁺ could quench the fluorescence of the blue emitters; Bi³⁺ and Al³⁺ could be differentiated by the yellow emitters, such as the fluorescence dropping for Bi³⁺, and the blue-shifted emission upon the addition of Al³⁺ with signal amplification. The different responses were considered to be associated with the various ligands on the two emitters. Moreover, this sensing system also exhibited good sensitivity and selectivity. Finally, the present method was used to detect Fe³⁺, Bi³⁺ and Al³⁺ in common drugs.